Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$148.45	10.831%	$164.5286	$164.53	$164.55	$164.50
Purchase #2	$21.34	12.240%	$23.952	$23.95	$23.95	$24.00
Purchase #3	$12.94	13.683%	$14.7106	$14.71	$14.70	$14.70
Purchase #4	$165.77	12.544%	$186.5642	$186.56	$186.55	$186.60
Purchase #5	$118.44	7.820%	$127.702	$127.70	$127.70	$127.70
Purchase #6	$77.47	7.327%	$83.1462	$83.15	$83.15	$83.10
Purchase #7	$85.38	5.509%	$90.0836	$90.08	$90.10	$90.10
7 purchase totals =	$629.79		$690.6872	$690.68	$690.70	$690.70